Manufacture of trialkylaluminium compounds



Patented Oct. 12, 1954 UNITED STATES PATENT OFFICE MANUFACTURE OF TRIALKYLALUIWINIUM COMPOUNDS No Drawing. Application May 12, 1953, Serial No. 354,658

Claims priority, application Germany May 13, 1952 7 Claims. (Cl. 260-448) .1 2 This invention relates to the manufacture of y havin approximately the composition of trialkylaluminium compounds. These com- AlzMg. By the latter reaction, if ethyl chloride pounds are also referred to as aluminium trialkyls.

Mixtures of alkylaluminium dihalides, RAlHalz, and dialkylaluminium monohalides, R2A1Ha1, known as alkylaluminium sesquihalides, may easily be obtained direct from aluminium and alkylhalides, as shown, for example, in the following equation:

As the reaction products are generally liquid or may be liquefied by a sli ht increase in temperature, the aluminium dissolves smoothly in the alkylhalide, and disturbances due to precipitation of a solid sediment do not occur.

If magnesium is alloyed to the aluminium, aluminium compounds with a low halogen content up to the halogen-free or nearly halogenfree aluminium trialkyls are obtained by the action of alkyl halides. According to A. V. Grosse and Mavity (J. Organic Chem., 1940, 5, 110 and 119) very homogeneous dialkylaluminium monohalides (in addition to magnesium halides) are obtained with Magnalium (70% Al, 30% Mg), and according to the process of German Patent application Z 2680 IVs/l2 o, filed on May 13, 1952, alloys of aluminium and magnesium containing 57-65% of magnesium, yield aluminium trialkyls directly as the main products.

In the last-mentioned process, however, the quantity of magnesium halide which is also formed is disproportionately great. For example, by the reaction of 1 mol. of MgsAlz (=126 g.) with ethyl bromide, the reaction product obtained, after conversion is complete, consists of 228 g. of triethylaluminium and 552 g. of magnesium bromide, and even when using ethyl chloride, the 228 g. of triethylaluminium are obtained mixed with 285 g. of magnesium chloride. Thus towards the end of the reaction, the reaction mixture becomes very viscous and dimculties may be encountered in stirring. The inadequate mixing which may thus result may lead to unsatisfactory progress of the reaction.

Though the process of German Patent application Z 2680 Ive/l2 o renders possible the direct production of aluminium trialkyls from magnesium-aluminium alloys and alkyl halides the possibility of providing a more smoothly operating process by working in two stages has been investigated, and more particularly, the production of alkylaluminium halides in a first stage followed by the conversion of these halides to aluminium trialkyls in a second stage.

As stated above, the sesquihalides may be produced from alkyl halides and aluminium and the dialkylaluminium monohalides may be produced according to Grosso and Mavity by using an alis used, the final product consists of liquid diethylaluminium chloride and magnesium chloride in the ratio 241:95 and this presents no difiiculties whatsoever.

The further conversion of the alkylaluminium halides to aluminium trialkyls has been effected by Grosse and Mavity who treated the halides referred to with sodium metal or potassium-sodium alloy at a high temperature. These reactions are exemplified by the equations;

However, the yields obtained by the latter conversion process are not very good. According to Grosse and Mavity they fluctuate between 40 and 60% of the theoretical yield.

It has now been found that the yields of aluminium trialkyls are considerably improved if the conversion or dehalogenation of the alkylaluminium halides is carried out with magnesium or magnesium-containing alloys, including such alloys containing aluminium, in a finely divided form. Particularly advantageous is the use of magnesium-aluminium alloys having the approximate composition of MgsAlz to MgzAl, and powdered to a dust-like fineness. At least of the theoretical yield of aluminium trialkyls, and frequently up to and more, is then consistently obtained.

From the point of view of ease of working it would appear to be immaterial whether AlzMgs is directly reacted with ethyl chloride according to the equation:

or whether a similar final result is achieved in two stages as follows:

Indeed, owing to the formation of 4 gram atoms of aluminium, the ratio of solid to liquid, which is of importance for the ease of mixing and stirring, is more unfavourable in the second case than in the first case.

In reality, however, it has been established that the two-stage procedure is much less subject to disturbance than is the more simple appearing one-stage procedure. In the second stage stirring of the batch is fully possible up to completion of the reaction. This is probably related to the fact that, since volatile alkyl halides are no longer present in the second stage, it is possible to raise the temperature during dehalogenation much higher (up to C.) than in the one-stage process and this has'a favourable effect on the form in which the magnesium halide separates. If, on completion of conversion, the aluminium trialkyl formed is distilled off, the magnesium halide, intimately mixed with finely dispersed aluminium, remains in the reaction vessel in a very loose form and can still be stirred even in the dry state. This is very favourable for the technical operation of the process.

Thus the invention consists in a process for the production of aluminium trialkyls, in which an alkylaluminium halide of the general formula AlXzY, in which X represents an alkyl rachcal and Y represents a halogen or vice versa, or a mixture of such halides is heated with finely divided magnesium or a finely divided magnesium alloy at a temperature of up to 180 C.

The invention also consists in a two-stage process for the production of aluminium trialkyls from alkyi halides, in which an alkyl halide is converted to an alkylaluminium halide or mixture of alkylaluminium halides and the alkylaluminium halide or mixture of alkylaluminium halides is then converted to an aluminium trialkyl by heating with finely powdered magnesium or magnesium alloy at a temperature of up to 180 C.

Consideration of the equations relating to both reactions of the two-stage process shows that on completion of the second stage just as much aluminium is present as was used in the first stage. A very economical process for the production of aluminium trialkyls, and especially of triethylaluminium, is thus provided if the following procedure is adopted.

Two similar reaction vessels fitted with stirring mechanisms are provided. A pre-determined quantity of aluminium is brought into solution with ethyl chloride in the first vessel, and the solution treated as described above with the requisite quantity of finely powdered magnesium-aluminium alloy. The final product, triethylaluminium, is distilled off from the vessel under nitrogen. Following this, and, if necessary, after the addition of a small quantity of "ethylaluminiumsesquibromide as catalyst, ethyl chloride is carefully introduced to the vessel whilst stirring and the aluminium is finally brought into solution at 100 120 0. with slow introduction of ethyl chloride. The sesquichloride now formed is in admixture with magnesium chloride and is therefore conveniently first distilled. It is collected in the second reaction vessel, in which the after-treatment with the magnesium-aluminium alloy is carried out. Whilst this is proceeding, the magnesium chloride in the first vessel is dissolved out with water and the vessel then prepared to receive the next charge of sesquichloride (distillate from vessel 2) so that an uninterrupted operation is possible, in which each kettle is alternately used for the production of the sesquichloride and of the triethylaluminium and which in practice uses only the alloy AlzMgs and alkyl halide. The process thus proceeds according to the Brutto (gross) equation of the one-stage process according to German Patent application Z 2680 IVc/ 12 0.

Even though the procedure just described has been shown to be particularly advantageous from the practical and commercial aspects, the detailed description of this individual method is not intended to restrict the scope of the invention in any way. On the contrary, the invention is based in general on the discovery that the conversion of alkylaluminium-halogen compounds to aluminium triallryls using finely divided magnesium and magnesium-containing alloys possesses outstanding advantages.

The information given in the above description is in such detail as to render any particular examples unnecessary. In supplementation, however, attention is drawn to the following.

Mixtures containing alkylaluminium dihalides, in particular bromides, react very strongly with the finely divided metals. The powdered magnesium or magnesium alloy should, therefore, be added to begin with in portions to such mixtures and the temperature carefully raised to C. and allowed to rise slowly above this, until the reaction taking place with a spontaneous increase in temperature is complete. The remainder of the magnesium or the alloy may be added and mixed and further heating may take place only after conversion of the dihalide portion to monohalide has taken place. The complete removal of the halogen necessitates heating to about C. for several hours. Above this temperature, losses due to decomposition have to be taken into account. Naturally, dehalogenation of the sesquihalides may be confined to the aluminiumdialkyl halide stage, by using a suitable procedure.

Isolation of the products obtained by this process by distillation (best carried out in vacuo) as described in the foregoing, is particularly convenient. This is, however, by no means the only method possible. Inert solvents may, for example, be used for the extraction, particularly hydrocarbons.

We claim:

1. Process for the production of aluminium trialkyls which comprises heating an alkyl aluminium halide with a finely divided metal containing magnesium at a temperature of up to C.

2. Process according to claim 1, in which an alkyl aluminium halide of the general formula AlXzY is used, wherein X represents an alkyl and Y represents a halogen.

3. Process according to claim 1, in which an alkyl aluminium halide compound of the general formula AIXYz is used, wherein X represents an alkyl and Y represents a halogen.

4. Process according to claim 1, in which the metal containin magnesium is magnesium itself.

5. Process according to claim 1, in which the metal containing magnesium is a magnesium al- 10y.

6. Process according to claim 5, in which the metal containing magnesium is a magnesiumaluminium alloy approximately composed according to the general formula AlzMgs.

'7. Process according to claim 1, in which the metallic aluminium obtained by the reaction is reacted with an alkyl halide into an alkyl aluminium halide and this alkyl aluminium halide is again used as the initial material.

References Cited in the file of this patent Wendt, Ben, vol. 56, pages 46642 (1923).

Reid et al., Chem. Soc. Jour. (1948), pages 1597-1601.

Grause et al., J. Org. Chem, vol 5, page 110. 

1. PROCESS FOR THE PRODUCTION OF ALUMINIUM TRIALKYLS WHICH COMPRISES HEATING AN ALKYL ALUMINIUM HALIDE WITH A FINELY DIVIDED METAL CONTAINING MAGNESIUM AT A TEMPERATURE OF UP TO 180* C. 